Nonrotating tacan antenna

ABSTRACT

This invention relates to a method of providing 15 cycle modulation in the distribution cavity of a non-rotating Tacan antenna, which antenna radiates a rotating cardioid radiation pattern. The H11 coaxial mode is induced in the cavity by separately injecting a sequential signal on diametrically opposed probes in the transformer by means of a switching device external to the transformer. The signals fed to each probe of a diametrically opposed pair are in phase opposition. This separate signal is obtained by extracting a part of the transmitter output signal or carrier signal prior to the transformer input. The fraction of the input signal is controlled to adjust the percentage of amplitude modulation at the output of the transformer. Prior to the transformer input the carrier signal is also acted upon by a phase compensator for optimizing the relative phase of the carrier and the 15 cycle modulation component. This arrangement permits separate control of the amplitude and phase of the modulation component with respect to the coexisting carrier component.

Unite States Patent n91 lden [451 Jan. 28, 1975 1 NONROTATING TACAN ANTENNA [75] Inventor: Floyd William lden, Pompton Plains, NJ.

International Telephone and Telegraph Corporation, Nutley. NJ.

[22] Filed: July 25, 1973 [21] App]. No.: 382,406

Related US. Application Data [73] Assignee:

Primary Examiner- Richard A. Farley Assistant Examiner-Richard E. Berger Attorney, Agent, or FirmJohn T. O'Halloran; Menotti J. Lombardi, Jr.; Vincent lngrassia [57] ABSTRACT This invention relates to a method of providing 15 cycle modulation in the distribution cavity of a nonrotating Tacan antenna. which antenna radiates a rotating cardioid radiation pattern. The H coaxial mode is induced in the cavity by separately injecting a sequential signal on diametrically opposed probes in the transformer by means of a switching device external to the transformer. The signals fed to each probe of a diametrically opposed pair are in phase opposition. This separate signal is obtained by extracting a part of the transmitter output signal or carrier signal prior to the transformer input. The fraction of the input signal is controlled to adjust the percentage of amplitude modulation at the output of the transformer. Prior to the transformer input the carrier signal is also acted upon by a phase compensator for optimizing the relative phase of the carrier and the 15 cycle modulation component. This arrangement permits separate control of the amplitude and phase of the modulation component with respect to the coexisting carrier component.

4 Claims, 6 Drawing Figures PATENTED 3.863.255

' SHEET 10F 2 mA/vsM/rrm v our ur k 5 I Qfiig. 4' 'u in INVENTOR 0.

FLOYO W. IDEA! DZW AGENT 1 NONROTATING TACAN ANTENNA This is a continuation of Application Ser. No. 152,132 filed June ll, l97l, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to a method for providing a rotating cardioid radiation pattern from a non-rotating antenna, and more particularly to a method of providing the required l5 cycle modulation in the distribution cavity of a non-rotating Tacan antenna.

The distribution cavity of a Tacan antenna consists of an RF impedance transformer coupled between the power source of the transmitter and a plurality of output cables connected around the periphery of the transformer at the low impedance end (at the opposite end from the feed point). These output cables feed a plurality of radiators located around the periphery of the Tacan antenna, said radiators being switched off sequentially to produce a desired 135 cycle modulation required in present Tacan Systems.

A known method of providing the cycle modulation is to excite the H coaxial mode of propagation in the cavity formed by the coaxial transformer by sequentially switching the ground connections of radially located probes projecting into the cavity from the outer wall of the transformer near its input end. As each probe is grounded it represents a disturbance which interacts with the existing TEM, or normal coaxial mode in the transformer to produce the desired I-I mode. This mode then propagates through the transformer to the output cables which supply signals to the radiators on the antenna. The phase of the TEM propagating mode changes linearly with frequency. The phase of the induced H propagating mode does not change linearly but has a variable rate of change which is slower than that of the TEM propagating mode.

When the above described method is employed, the phase relationship between the input carrier and the induced H propagating mode is optimum at only one frequency, which frequency is determined by design considerations. At its worst, this can result in a radiated signal which is either completely lacking in amplitude modulation or one in which the amplitude modulation is excessive.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of modulating a carrier signal within the distribution cavity of a non-rotating antenna by means of an external switching device.

Acccording to a broad aspect of the invention, there is provided a method of modulating a transmitter carrier signal in the distribution cavity of a non-rotating antenna, which antenna produces a rotating cardioid radiation pattern comprising extracting a predetermined portion of said transmitter carrier signal prior to the input of said distribution cavity; adjusting the phase of said extracted signal; injecting said phase adjusted signal sequentially to a plurality of pairs of probes projecting into the distribution cavity to excite the H coaxial mode of propagation in the cavity, each probe of each pair being diametrically opposed and said excitation on each probe of each pair is in phase opposition; delaying the remainder of said carriersignal by an integral number of wavelengths to produce a desired phase relationship between said carrier signal and said H mode; feeding said delayed carrier signal to the center conductor of an RF impedance transformer located within said distribution cavity; and extracting signals having the desired modulation amplitude and phase from the outputs of said transformer.

The above and other objects of the present invention will be better understood from the following detailed description taken in conjunction with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a rotating cardioid radiation pattern radiated by present Tacan antennas;

FIG. 2 shows the circular surface of a Tacan antenna having an array of radiators located around its periphery;

FIG. 3 shows an arrangement for modulating the transmitter output signal within the distribution cavity of a Tacan antenna according to the prior art;

FIG. 4 illustrates the phase shift relationship between the carrier signal, or TEM coaxial mode of propagation and an induced I-I coaxial mode of propagation within the distribution cavity of FIG. 3;

FIG. 5 shows an arrangement for modulating the carrier signal within the distribution cavity of a Tacan antenna according to the inventive method; and

FIG. 6 shows the phase shift relationship of the carrier signal and the induced H, propagating mode along the distribution cavity of the arrangement shown in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a rotating cardioid pattern having a cycle modulation component superimposed thereon for meeting the requirements of present Tacan systems.

The 135 cycle modulation component is generated by sequentially turning off radiators 1 located on the periphery of antenna 2 shown in FIG. 2. Radiators I are coupled to the low impedance end of the RF impedance transformer. The technique of producing the above described 135 cycle modulation by the sequential turning off of an array of radiators on the antenna is well known and need not be further described.

FIG. 3 shows a distribution cavity 3 of a Tacan antenna having a plurality of radially located probes 4 projecting in from the outer wall of the transformer. In this case the H coaxial mode of propagation in the cavity is induced by sequentially grounding each of the radially located probes 4. At any one time, only one probe is grounded and acts as a disturbance in the distribution cavity which interacts with the normal TEM coaxial mode to produce the H mode of propagation. The 15 cycle modulation required in Tacan systems is assured by placing the appropriate number of probes in the distribution cavity. The transmitter output, or carrier signal, is fed into center conductor 5 and the outputs 6, at the low impedance end of the transformer, are coupled to the radiators 1 located on the periphery of antenna 2.

The TEM mode, or the normal coaxial mode in the transformer propagates along the distribution cavity, and its phase shift is a linear function of frequency as shown by'curve A in FIG. 4. The H mode induced by probes 4 also propagate through the distribution cavity; however, its phase shift is a variable function of frequency, also shown by curve B in FIG. 4.

It can be seen from FIG. 4 that the phase shift of the H mode along the distribution cavity shifts at a slower rate than that of the normal TEM mode, and that they are in phase at only one frequency denoted in FIG. 4. The point of intersection of the two curves is fixed by choosing the proper design considerations of the RF transformer, distribution cavity and location of the probes.

FIG. 5 shows an arrangement which provides for the excitation of the same H mode by separately injecting a signal on a plurality of pairs of radial probes 11 (capacitive or inductive) such that the excitation on each probe of each pair is in phase opposition. This is accomplished by means of a switching device 12 external to the distribution cavity 3. This separate signal is obtained by extracting a part of the transmitter output signal prior to the transformer input; the fraction of the signal extracted being controlled by power divider 8. Power divider 8 may contain a variable attenuator which can be adjusted to control the amount of signal extracted thereby controlling the percentage of amplitude modulation at the outputs 6 of the transformer. The output of power divider 8 is coupled to a phase adjuster 10 which has the capability of changing the phase of the extracted signal over a range of 360. The output of phase adjuster 10 is coupled to the terminals of commutator 12, each of which are sequentially coupled to radial probes 11. In this manner the H mode is induced in the distribution cavity 3. By adjusting the phase of the extracted signal it can be assured that the phase of the induced H mode and the phase of the existing TEM mode are the same at least one frequency. To provide the required phase opposition, one of the commutator terminals is one-half wavelength longer than the other as illustrated in FIG. 5. The commutator 12 rotates at a rate of 15 revolutions per second to produce the 15 Hzs modulation of the standard Tacan singal.

That part of the carrier signal which has not been extracted is coupled to the center conductor 5 of the RF transformer via phase compensator 9 which may consist of coaxial cable having a length equal to an integral multiple of wavelengths. This will reduce the slope of the phase shift versus frequency characteristic of the TEM mode propagating in the distribution cavity. This is illustrated in FIG. 6, curve A representing the phase shift with frequency of the normal TEM mode, and curve B representing the phase shift with frequency of the H mode. There are now two points of intersection at which the phases of the two propagating modes are equal denoted by x and y. These points of inersection represent those points at which the relative phase of the carrier and the 15 cycle modulation component is optimum at the transformer outputs 6. The probes 11 may be fed singly or as out-of-phase diametrical pairs.

Using the above described inventive method, the relative phase relationship between the TEM mode and the induced H mode can be phase adjusted such that an optimum relationship exists at the outputs 6 of the transformer at any desired frequency within the range of operating frequencies of the system.

It is to be understood that the foregoing description of this invention is made by way of example only and is not to be considered as a limitation of its scope.

1 claim:

1. A method of modulating a transmitter carrier sig- 5 nal in the distribution cavity of a non-rotating antenna.

which antenna produces a rotating cardioid radiation pattern comprising:

extracting a predetermined portion of said transmitter carrier signal prior to the input of said distribu- 10 tion cavity;

adjusting the phase of said extracted signal;

injecting said phase adjusted signal sequentially to a plurality of pairs of probes projecting into the distribution cavity to excite the H coaxial mode of 15 propagation in the cavity, each probe of each pair being diametrically opposed and said excitation on each probe of each pair is in phase opposition;

delaying the remainder of said carrier signal by an integral number of wavelengths to produce a desired phase relationship between said carrier signal and said H mode;

feeding said delayed carrier signal to the center conductor of an RF impedance transformer located within said distribution cavity; and

extracting signals having the desired amplitude and phase modulation from the outputs of said transformer.

2. A method according to claim 1 wherein said probes are capacitive probes.

3. A method according to claim 1 wherein said probes are inductive probes.

4. An arrangement for modulating a transmitter carrier signal in the distribution cavity of a nonrotating antenna, which antenna produces a rotating cardioid radiation pattern comprising:

means for extracting a predetermined portion of said carrier signal prior to the input of said distribution cavity;

means for adjusting the phase of said extracted signal;

a plurality of pairs of probes projecting into said dis tribution cavity;

means for injecting said phase adjusted signal sequentially to said plurality of pairs of probes projecting into the distribution cavity to excite H coaxial mode of propagation in the cavity, each probe of each pair being diametrically opposed and said excitation on each probe of each pair is in phase opposition;

means for delaying the remainder of said carrier signal by an integral number of wavelengths to produce a desired phase relationship between said carrier signal and said H mode;

an RF impedance transformer having a center conductor, said transformer located within said distribution cavity;

means for feeding said delayed carrier signal to said center conductor; and

,0 means for extracting signals having the desired amplitude and phase modulation.

LII 

1. A method of modulating a transmitter carrier signal in the distribution cavity of a non-rotating antenna, which antenna produces a rotating cardioid radiation pattern comprising: extracting a Predetermined portion of said transmitter carrier signal prior to the input of said distribution cavity; adjusting the phase of said extracted signal; injecting said phase adjusted signal sequentially to a plurality of pairs of probes projecting into the distribution cavity to excite the H11 coaxial mode of propagation in the cavity, each probe of each pair being diametrically opposed and said excitation on each probe of each pair is in phase opposition; delaying the remainder of said carrier signal by an integral number of wavelengths to produce a desired phase relationship between said carrier signal and said H11 mode; feeding said delayed carrier signal to the center conductor of an RF impedance transformer located within said distribution cavity; and extracting signals having the desired amplitude and phase modulation from the outputs of said transformer.
 2. A method according to claim 1 wherein said probes are capacitive probes.
 3. A method according to claim 1 wherein said probes are inductive probes.
 4. An arrangement for modulating a transmitter carrier signal in the distribution cavity of a nonrotating antenna, which antenna produces a rotating cardioid radiation pattern comprising: means for extracting a predetermined portion of said carrier signal prior to the input of said distribution cavity; means for adjusting the phase of said extracted signal; a plurality of pairs of probes projecting into said distribution cavity; means for injecting said phase adjusted signal sequentially to said plurality of pairs of probes projecting into the distribution cavity to excite H11 coaxial mode of propagation in the cavity, each probe of each pair being diametrically opposed and said excitation on each probe of each pair is in phase opposition; means for delaying the remainder of said carrier signal by an integral number of wavelengths to produce a desired phase relationship between said carrier signal and said H11 mode; an RF impedance transformer having a center conductor, said transformer located within said distribution cavity; means for feeding said delayed carrier signal to said center conductor; and means for extracting signals having the desired amplitude and phase modulation. 